The long-term objective of this proposal is to clarify the causes of the prevalence of obesity in black women. The specific aims of this proposal are: 1) To investigate whether there is a defect in thermogenesis in black women in comparison to white women and 2) To determine if differences exist in fat cell morphology and/or fat cell metabolism between black and white women which may produce a differing metabolic milieu predisposing to the development of the complications of obesity in black women. The resting metabolic rate (RMR), and after a standard meal, the thermic effect of food (TEF) and the nutrients oxidized and stored, will be measured in 48 black and 48 white women of similar obesity and age. Black and white women volunteers between the ages of 30 and 45 will be divided into 3 groups of 16 each: 95-105%, 120-134%, and 135-150% of ideal weight. Body composition will be measured by hydrodensitometry. Any differences between black and white women in RMR, TEF, the nutrient oxidized after a mixed meal or the proportions of nutrients stored will be documented, as will the relation of these measures to body weight, fat free mass, and body surface area. In a second set of studies, 32 black and 32 white obese women who are between 130 and 150% of their ideal body weight will be selected on the basis of their body fat distribution, so that half will have upper body obesity and half lower body obesity (determined by measuring their waist-to-hip ratio). This will be done in order to have enough women with upper body obesity in the study groups, since there is a greater incidence of the complications of obesity in persons with upper body obesity. The morphology and the in vitro metabolism of fat cells obtained from three subcutaneous sites (epigastric, hypogastric, and gluteal) will be studied. Basal and stimulated lipolysis, basal and insulin- stimulated glucose transport, glucose oxidation, lipogenesis from glucose, and lipoprotein lipase activity will be measured. Other tests will be performed to further characterize upper and lower body obesity. Plasma sex hormones (estradiol, free-testosterone, and testosterone-estradiol-binding globulin) will be assayed to determine if they correlate with distribution of body fat and are different in black and white women. In vivo insulin sensitivity will be measured to determine if the distribution of body fat is positively correlated with insulin resistance and if there are differences between black and white women. Gas-liquid chromotography of fatty acid patterns will be done to see if there are any differences between the races. These studies may be significant in providing initial clues to explain the high prevalence of obesity in black women.